Effects of magnetic shear and thermodynamic asymmetry on spontaneous MHD magnetic reconnection

TL;DR

This study uses 2D MHD simulations to explore how magnetic shear and thermodynamic asymmetry influence spontaneous magnetic reconnection, revealing effects on shock formation, plasma mixing, and reconnection rates.

Contribution

It provides new insights into the impact of magnetic shear and thermodynamic asymmetry on reconnection dynamics and rates, extending previous symmetric models.

Findings

Fast-mode shock weakens with magnetic shear.

Plasma from both sides mixes in the longer plasmoid.

Reconnection rate decreases drastically due to asymmetry and shear.

Abstract

The spontaneous evolution of magnetic reconnection in generalized situations (with thermodynamic asymmetry regarding the current sheet and magnetic shear) is investigated using two-dimensional magnetohydrodynamic simulation. We focus on the asymptotic state of temporal evolution, i.e., the self-similarly expanding phase (Nitta et al. 2001). 1) A long fast-mode shock is generated in front of the shorter plasmoid as in the shear-less thermodynamically asymmetric case; however, the sheared magnetic component weakens the shock. This fast shock may work as a particle acceleration site. 2) The shorter plasmoid-side plasma infiltrates the longer plasmoid across the current sheet. Then, the plasmas from both sides of the current sheet coexist on the same magnetic field lines in the longer plasmoid. This may result in efficient plasma mixing. 3) The thermodynamic asymmetry and magnetic shear drastically decrease the reconnection rate in many orders of magnitude.